Precisely shaped particles and method of making the same

ABSTRACT

A coated abrasive article comprising: 
     (a) a backing; 
     (b) at least one layer comprising a plurality of precisely shaped abrasive particles that comprise abrasive grits and a free-radically polymerized binder, wherein said precisely shaped particles have vertexes and 
     (c) a bonding medium which serves to adhere said precisely shaped particles to said backing; 
     wherein the precisely shaped particles are randomly disposed on the backing such that at least a portion of said particles are oriented with said vertexes pointing toward said backing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to particulate material comprising a binder, anda method for making same. When the particulate material further containsabrasive grits, it can be used in bonded abrasives, coated abrasives,and nonwoven abrasives.

2. Discussion of the Art

Conventional coated abrasive articles typically consist of a layer ofabrasive grits adhered to a backing. Generally only a small fraction ofthe abrasive grits in this layer are actually utilized during the usefullife of the coated abrasive article. A large proportion of the abrasivegrits in this layer are wasted. Furthermore, the backing, one of themore expensive components of the coated abrasive article, must also bedisposed of before it has worn out.

Many attempts have been made to distribute the abrasive grits on thebacking in such a manner so that a higher percentage of abrasive gritsare actually utilized, thereby extending the useful life of the coatedabrasive article. By extending the life of the coated abrasive article,fewer belt or disc changes are required, thereby saving time andreducing labor costs. Merely depositing a thick layer of abrasive gritson the backing will not solve the problem, because grits lying below thetopmost grits are not likely to be used.

Several methods whereby abrasive grits can be distributed in a coatedabrasive article in such a way as to prolong the life of the article areknown. One such way involves incorporating abrasive agglomerates in thecoated abrasive article. Abrasive agglomerates consist of abrasive gritsbonded together by means of a binder to form a mass. The use of abrasiveagglomerates having random shapes and sizes makes it difficult topredictably control the quantity of abrasive grits that come intocontact with the surface of a workpiece. For this reason, it would bedesirable to have an economical way to prepare precisely shaped abrasiveagglomerates.

SUMMARY OF THE INVENTION

This invention provides precisely shaped particles and methods formaking these particles. The particles comprise a binder. In onedesirable embodiment, a plurality of abrasive grits is dispersed in thebinder.

The method of this invention comprises the steps of:

(a) providing a production tool having a three-dimensional body whichhas at least one continuous surface, said surface containing at leastone opening formed in said continuous surface, said at least one openingproviding access to a cavity in said three-dimensional body;

(b) providing a dispensing means capable of introducing a binderprecursor comprising a thermosetting resin into said at least one cavitythrough said at least one opening;

(c) providing a means, within a curing zone, for at least partiallycuring said binder precursor;

(d) introducing said binder precursor into at least a portion of said atleast one cavity;

(e) continuously moving said at least one cavity through said curingzone to at least partially cure said binder precursor to provide asolidified, handleable binder having a shape corresponding to thatportion of the cavity into which the binder precursor had beenintroduced;

(f) removing said binder from said at least one cavity; and

(g) converting said binder to form a precisely shaped particle.

Steps (f) and (g) can be conducted simultaneously.

In a preferred embodiment, a plurality of abrasive grits is includedwith the binder precursor in step (d), and a binder containing abrasivegrits is formed in step (e). The binder that contains abrasive grits isremoved from the at least one cavity of the production tool in step (f).Materials other than abrasive grits can be included with the binderprecursor.

The curing zone can contain a source of thermal energy, a source ofradiation energy, or both. Suitable sources of radiation energy includeelectron beam, visible light, and ultraviolet light. In a variation ofthe general method, curing can be effected by thermal energy or by acombination of radiation energy and thermal energy.

In both the general and preferred embodiments, it is preferred thatsteps (d), (e), and (f) be carried out on a continuous basis or becarried out in a continuous manner. For these embodiments, it ispreferred that the production tool be an endless web (belt), or a drum,preferably a cylindrical drum, which will rotate about its axis.Alternatively, a web having two ends can be used. Such a two-ended webtravels from an unwind station to a rewind station. It is preferred thatthe production tool have a plurality of cavities.

During step (e) of the method, the binder precursor is solidified so asto be converted into a handleable binder.

The binder can be converted into particles by several means. In onemeans, when the binder is removed from the cavities of the productiontool, it is released in the form of individual particles. Theseparticles can contain additional materials or be free of additionalmaterials. A typical material that can be included in these particles isabrasive grits. The resulting particles preferably have shapes that areessentially the same as the shapes of the cavities of the productiontool. Thus, the particles have shapes that are determined by the shapesof the cavities of the production tool. In this first means, steps (f)and (g) are accomplished simultaneously, because the shaped particleshave their characteristic form when they are released from the cavitiesof the production tool.

In a second means, the binder is removed from the major surface of theproduction tool in the form of a sheet comprising shaped portions thatare of essentially of the same size and shape of the cavities of theproduction tool, but joined together by a relatively thin connectinglayer of the material of the binder. In this second means, the sheet isthen broken or crushed along the thin connecting layer of bindermaterial to form the particulate material of this invention. Theparticles can be screened or classified to a desired size distribution.If the connecting layer of the binder material is carefully broken orcrushed, the resulting particles can have shapes that are essentiallythe same as those of the cavities of the production tool.

It is also within the scope of this invention to use a carrier web todeliver binder precursor to the production tool. The binder precursorcan be coated onto one major surface, e.g., the front surface, of acarrier web and then the resulting coated carrier web is brought intocontact with the continuous surface of the production tool that containsthe cavities. After at least partial curing, i.e. solidifying, of thebinder precursor in the production tool, the binder, whichpreferentially adheres to the surface of the carrier web, is removedfirst from the production tool and then from the carrier web.Alternatively, the binder precursor is coated onto the continuoussurface of the production tool having cavities, whereby such cavitiesare filled, and the carrier web is brought into contact with thecontinuous surface of the production tool containing the binderprecursor in such a manner that the binder precursor contained in thecavities contacts the surface of the carrier web. After at least partialcuring, i.e. solidifying, of the binder precursor, the binder adheres tothe surface carrier web rather than to the production tool. The bindercan then be removed from the carrier web. Subsequently, the preciselyshaped particles are formed.

The precisely shaped particles can be modified by means of additives foruse in abrading applications, either by themselves or as a component ofan abrasive article. The particles of this invention can be used toprepare abrasive articles comprising a plurality of shaped particles,each of which comprises at least one abrasive grit and a binder, inwhich the binder is formed from a binder precursor comprising athermosetting resin that can be cured by radiation energy or thermalenergy or both. The particles can be bonded together to form a shapedmass, e.g., a wheel; alternatively, the particles can be bonded to abacking to form a coated abrasive article; or the particles can bebonded into a fibrous, nonwoven substrate to form a non-woven abrasivearticle.

This invention makes it possible to design particles suitable forspecific applications by varying the shape and composition of theparticles. The process of this invention provides a simple, fast, andeconomical method for manufacturing particles, especially abrasiveparticles having a precise shape. The process of this invention makes itpossible to accurately make abrasive particles having the samedimensions from batch to batch, thereby leading to more consistentabrasive articles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, and 3 are schematic side views illustrating various methodsof carrying out the process of this invention.

FIGS. 4 and 5 are schematic side views in elevation of a coated abrasivearticle that utilizes the particles of this invention.

FIG. 6 is a perspective view of a segment of the production tool ofFIG. 1. The segment illustrated in FIG. 6 is substantially similar tosegments of the production tools of FIGS. 1, 2, and 3.

FIG. 7 is a Scanning Electron Photomicrograph of a shaped abrasiveparticle made according to the process of this invention. The particlehas the shape of a triangular-based pyramid.

FIGS. 8 and 9 are schematic side views illustrating other methods ofcarrying out the process of this invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the expression "binder precursor" means any materialthat is conformable or can be made to be conformable by heat or pressureor both and that can be rendered non-conformable by means of radiationenergy or thermal energy or both. As used herein, the expression"solidified, handleable binder" means a binder precursor that has beenpolymerized or cured to such a degree that it will not substantiallyflow or experience a substantial change in shape. The expression"solidified, handleable binder" does not mean that the binder precursoris always fully polymerized or cured, but that it is sufficientlypolymerized or cured to allow removal thereof from the production toolwhile the production tool continues to move, without leading tosubstantial change in shape of the binder. After the binder is removedfrom the production tool, the binder can be exposed to an additionalenergy source to provide additional cure or polymerization of thebinder. As used herein, the term "binder" is synonymous with theexpression "solidified, handleable binder".

In one aspect, this invention involves a method of making a particulatematerial. In another aspect, this invention involves precisely shapedparticles comprising a solidified, handleable binder. In still anotheraspect, this invention involves abrasive articles, such as bondedabrasive articles, coated abrasive articles, and nonwoven abrasivearticles that comprise the precisely shaped particulate material of thisinvention.

FIG. 1 illustrates an apparatus capable of carrying out the method ofthis invention to make the particles of this invention. In apparatus 10,binder precursor 12 is fed by gravity from a hopper 14 onto a productiontool 16, which is in the form of an endless belt. The belt 16 travelsover two rolls 18, 20, at least one of which is power driven. FIG. 6 isa perspective view of a segment of the production tool 16. As can beseen in FIG. 6, the production tool 16 is a three-dimensional bodyhaving a continuous surface 21 containing an opening 22 that providesaccess to a cavity 23 in the three-dimensional body. The binderprecursor 12 fills at least a portion of cavity 23. The binder precursor12 then travels through a curing zone 24 where it is exposed to anenergy source 25 to at least partially cure the binder precursor 12 toform a solidified, handleable binder. Particles of precisely shapedbinder material 26 are removed from the production tool 16 and collectedin a container 28. External means 29, e.g., ultrasonic energy, can beused to help release the particles of binder material 26 from theproduction tool 16. Debris left in the production tool can be cleanedaway before any fresh binder precursor is fed to the production tool.

FIG. 2 illustrates another variation of apparatus capable of carryingout the method of this invention. Apparatus 30 comprises a carrier web32 which is fed from an unwind station 34. Unwind station 34 is in theform of a roll. The carrier web 32 can be made of a material such aspaper, cloth, polymeric film, nonwoven web, vulcanized fibre,combinations thereof and treated versions thereof. The preferredmaterial for the carrier web 32 is a polymeric film, such as, forexample, a polyester film. In FIG. 2, the carrier web 32 is transparentto radiation. A binder precursor 36 is fed by gravity from a hopper 38onto a major surface of the carrier web 32. The major surface of thecarrier web 32 containing the binder precursor 36 is forced against thesurface of a production tool 40 by means of a nip roll 42. The surfaceof the production tool 40 that contacts the carrier web is curved, butit is otherwise identical to that of the segment of the production toolshown in FIG. 6. The nip roll 42 also aids in forcing the binderprecursor 36 into the cavities of the production tool 40. The binderprecursor 36 then travels through a curing zone 43 where it is exposedto an energy source 44 to at least partially cure the binder precursor36 to form a solidified, handleable binder. Next, the carrier web 32containing the solidified, handleable binder is passed over a nip roll46. There must be sufficient adhesion between the carrier web 32 and thesolidified, handleable binder in order to allow for subsequent removalof the binder from the cavities of the production tool 40. The particlesof binder material 48 are removed from the carrier web 32 and collectedin a container 50. External means 51, e.g., ultrasonic energy, can beused to help release the particles 48 from the carrier web 32. Thecarrier web 32 is then recovered at rewind station 52 so that it can bereused. Rewind station 52 is in the form of a roll.

Removal of the particles of binder material from the carrier web can becarried out efficiently by an alternative method. In this alternative,the carrier web can contain a thin, water-soluble layer on the majorsurface thereof that receives the binder precursor 36 from the hopper38. The water-soluble layer will come into contact with the binderprecursor 36. After the binder precursor 36 is at least partially cured,the combination of carrier web 32 and solidified, handleable binder issubjected to a source of water, whereby the water dissolves thewater-soluble layer on the carrier web 32, thereby bringing aboutseparation of the particles of binder material from the carrier web 32.An example of a water-soluble layer useful for this variation is a layerof a water-soluble polymer, e.g., polyvinyl alcohol, polyvinylpyrrolidone, cellulose derivatives.

FIG. 3 illustrates another variation of an apparatus capable of carryingout the method of this invention. In apparatus 70, binder precursor 72is knife coated from a hopper 74 onto a production tool 76. Theproduction tool is in the form of a cylindrical drum and has an axis 78.The continuous surface of the production tool 76 is curved, but it isotherwise identical to the segment of the production tool shown in FIG.6. As the production tool 76 rotates about the axis 78, the binderprecursor 72 travels through a curing zone 79 where it is exposed to anenergy source 80 to at least partially cure the binder precursor 72 toform a solidified, handleable binder. Next, the particles of solidified,handleable binder 82 resulting from the curing step of the process areremoved from the production tool 76 and collected in a hopper 84.Removal is preferably carried out by mechanical means, e.g., a waterjet. It is preferred that any debris remaining in the production tool 76be removed before any fresh binder precursor is introduced. Debrisremoval can be accomplished by a brush, an air jet, or any otherconventional technique. Although not shown in FIG. 3, additional meanscan be used to aid in removing the particles of binder from theproduction tool 76.

The production tool is a three-dimensional body having at least onecontinuous surface. The continuous surface contains at least oneopening, preferably a plurality of openings, formed in the continuoussurface. Each opening provides access to a cavity formed in thethree-dimensional body. As used in this context, the term "continuous"means characterized by uninterrupted extension in space; the openingsand cavities are features in the continuous surface, but they do notbreak the surface into a plurality of individual surfaces. Theproduction tool can be in the form of a web, a belt, e.g., an endlessbelt, a sheet, a coating roll, or a sleeve mounted on a coating roll. Itis preferred that the production tool be one that allows continuousoperations, such as, for example, an endless belt or a cylindricalcoating roll that rotates about an axis. Typically, a cylindricalcoating roll is in the form of a right cylinder, has a diameter of fromabout 25 to about 45 cm, and is constructed of a rigid material.Apparatus utilizing a two-ended web can also be adapted to providecontinuous operations. The preferred materials for a production tool arepolymers, such as polyolefins, e.g., polypropylene, or metals, such asnickel. The production tool can also be formed from a ceramic material.

A production tool made of metal can be fabricated by engraving,photolithography, hobbing, etching, knurling, assembling a plurality ofmetal parts machined in the desired configuration, die punching, orother mechanical means, or by electroforming. The preferred method forpreparing a metal production tool or master tool is diamond turning.These techniques are further described in the Encyclopedia of PolymerScience and Technology, Vol. 8, John Wiley & Sons, Inc. (1968), p.651-665, and U.S. Pat. No. 3,689,346, col. 7, lines 30 to 55, both ofwhich are incorporated by reference. The production tool may alsocontain a release coating to permit easier removal of the binder fromthe cavities and to minimize wear of the production tool. Examples ofsuch release coatings include hard coatings such as metal carbides,metal nitrides, metal borides, diamond, or diamond-like carbon. It isalso within the scope of this invention to use a heated production tool,which is preferably made from metal. A heated tool may allow easierprocessing, more rapid curing, easier release of the shaped particlesfrom the tool.

In some instances, a polymeric production tool can be replicated from anoriginal master tool. This is especially preferred when the productiontool is in the form of a belt or web. One advantage of polymeric toolsover metal tools is cost. Another advantage of polymeric tools is thecapability of allowing radiation to pass from the radiation sourcethrough the production tool and into the binder precursor. A polymericproduction tool can be prepared by coating a molten thermoplastic resin,such as polypropylene, onto the master tool. The molten resin can thenbe quenched to give a thermoplastic replica of the master tool. Thispolymeric replica can then be utilized as the production tool.Additionally, the surface of the production tool may contain a releasecoating, such as a silicone-based material or a fluorochemical-basedmaterial, to improve the releasability of the binder from the productiontool. It is also within the scope of this invention to incorporate arelease agent into the polymer from which the production tool is formed.Typical release agents include silicone-based materials andfluorochemical-based materials. It is within the scope of this inventionto prepare production tools from polymers that exhibit good releasecharacteristics. Such a polymer is described in WO 9215626, publishedSep. 17, 1992, incorporated herein by reference. That referencedescribes a fluorochemical graft copolymer comprising: a base polymercomprising polymerized units derived from monomers having terminalolefinic double bonds, having a moiety comprising a fluoroaliphaticgroup grafted thereto. The grafted fluoroaliphatic group is generallyderived from a fluorochemical olefin comprising a fluoroaliphatic groupand a polymerizable double bond.

The fluoroaliphatic group of the fluorochemical olefin is generallybonded to the polymerizable double bond through a linking group. Suchfluorochemical olefins can be represented by the following formula:

    (R.sub.f).sub.a Q(CR═CH.sub.2).sub.b

wherein R represents hydrogen, trifluoromethyl, or straight-chain orbranched-chain alkyl group containing 1 to 4 carbon atoms;

a represents an integer from 1 to 10;

b represents an integer from 1 to 6;

Q represents an (a+b)-valent linking group that does not substantiallyinterfere with free radical polymerization; and

R_(f) represents a fluoroaliphatic group comprising a fully fluorinatedterminal group containing at least seven fluorine atoms.

The metal master tool can be made by the same methods that can be usedto make metal production tools. Other methods of preparing productiontools are described in assignee's copending application Ser. No.08/004,929, filed Jan. 14, 1993, now abandoned incorporated herein byreference.

If the production tool is made from a thermoplastic material, theconditions of the method should be set such that any heat generated inthe curing zone does not adversely affect the production tool.

At least one continuous surface of the production tool contains at leastone cavity, preferably a plurality of cavities. The solidified,handleable binder precursor will acquire a shape corresponding to theshape of the cavity. A cavity can have any geometric shape such as apyramid, prism, cylinder, cone, or thin body having opposed polygonalfaces. The geometric shapes can be truncated versions of the foregoing.It is also within the scope of this invention that a given productiontool may contain a variety of cavities of different shapes or cavitiesof different sizes or both. In the case of a web or belt, the cavity canextend completely through the production tool. The cavities can abutt orhave land areas between them. It is preferred that the sides of thecavities have a slope associated them to allow easier removal of thebinder from the production tool.

Binder precursors suitable for this invention comprise a thermosettingresin that is capable of being cured by radiation energy or thermalenergy. The binder precursor can polymerize via a condensation curingmechanism or an addition mechanism. The preferred binder precursorspolymerize via an addition mechanism. The binder precursor canpolymerize via a free radical mechanism or a cationic mechanism or bothmechanisms. The binder precursor can be unfilled or can containconventional filler material.

The binder precursor is preferably capable of being cured by radiationenergy or thermal energy. Sources of radiation energy include electronbeam energy, ultraviolet light, visible light, and laser light. Ifultraviolet or visible light is utilized, a photoinitiator is preferablyincluded in the mixture. Upon being exposed to ultraviolet or visiblelight, the photoinitiator generates a free radical source or a cationicsource. This free radical source or cationic source then initiates thepolymerization of the binder precursor. A photoinitiator is optionalwhen a source of electron beam energy is utilized.

Examples of binder precursors that are capable of being cured byradiation energy include acrylated urethanes, acrylated epoxies,ethylenically unsaturated compounds, aminoplast derivatives havingpendant unsaturated carbonyl groups, isocyanurate derivatives having atleast one pendant acrylate group, isocyanate derivatives having at leastone pendant acrylate group, vinyl ethers, epoxy resins, and combinationsthereof. The term acrylate includes both acrylates and methacrylates.

Acrylated urethanes are diacrylate esters of hydroxy terminatedisocyanate extended polyesters or polyethers. Examples of commerciallyavailable acrylated urethanes include "UVITHANE 782", available fromMorton Thiokol Chemical, and "CMD 6600", "CMD 8400", and "CMD 8805",available from Radcure Specialties.

Acrylated epoxies are diacrylate esters of epoxy resins, such as thediacrylate esters of bisphenol A epoxy resin. Examples of commerciallyavailable acrylated epoxies include "CMD 3500", "CMD 3600", and "CMD3700", available from Radcure Specialties.

Ethylenically unsaturated compounds include both monomeric and polymericcompounds that contain atoms of carbon, hydrogen and oxygen, andoptionally, nitrogen and the halogens. Oxygen or nitrogen atoms or bothare generally present in ether, ester, urethane, amide, and urea groups.Ethylenically unsaturated compounds preferably have a molecular weightof less than about 4,000 and are preferably esters resulting from thereaction of compounds containing aliphatic monohydroxy groups oraliphatic polyhydroxy groups and unsaturated carboxylic acids, such asacrylic acid, methacrylic acid, itaconic acid, crotonic acid,isocrotonic acid, maleic acid, and the like. Representative examples ofacrylates include methyl methacrylate, ethyl methacrylate, ethyleneglycol diacrylate, ethylene glycol methacrylate, hexanediol diacrylate,triethylene glycol diacrylate, trimethylolpropane triacrylate, glyceroltriacrylate, pentaerthyitol triacrylate, pentaerythritol methacrylate,and pentaerythritol tetraacrylate. Other ethylenically unsaturatedcompounds include monoallyl, polyallyl, and polymethylallyl esters andamides of carboxylic acids, such as diallyl phthalate, diallyl adipate,and N,N-diallyladipamide. Still other ethylenically unsaturatedcompounds include styrene, divinyl benzene, and vinyl toluene. Othernitrogen-containing, ethylenically unsaturated compounds includetris(2-acryloyl-oxyethyl)isocyanurate,1,3,5-tri(2-methyacryloxyethyl)-s-triazine, acrylamide,methylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide,N-vinylpyrrolidone, and N-vinylpiperidone.

The aminoplast can be monomeric or oligomeric. The aminoplast resinshave at least one pendant α,β-unsaturated carbonyl group per molecule.These α,β-unsaturated carbonyl groups can be acrylate, methacrylate, oracrylamide groups. Examples of such resins includeN-hydroxymethyl-acrylamide, N,N'-oxydimethylenebisacrylamide, ortho andpara acrylamidomethylated phenol, acrylamidomethylated phenolic novolac,and combinations thereof. These materials are further described in U.S.Pat. No. 4,903,440 and U.S. Ser. No. 07/659,752, filed Feb. 24, 1991,now U.S. Pat. No. 5,236,472 both of which are incorporated herein byreference.

Isocyanurate derivatives having at least one pendant acrylate group andisocyanate derivatives having at least one pendant acrylate group arefurther described in U.S. Pat. No. 4,652,274, incorporated herein byreference. The preferred isocyanurate material is a triacrylate oftris(hydroxy ethyl) isocyanurate.

Examples of vinyl ethers suitable for this invention include vinyl etherfunctionalized urethane oligomers, commercially available from AlliedSignal under the trade designations "VE 4010", "VE 4015", "VE 2010", "VE2020", and "VE 4020".

Epoxies have an oxirane ring and are polymerized by the ring opening.Epoxy resins include monomeric epoxy resins and polymeric epoxy resins.These resins can vary greatly in the nature of their backbones andsubstituent groups. For example, the backbone may be of any typenormally associated with epoxy resins and substituent groups thereon canbe any group free of an active hydrogen atom that is reactive with anoxirane ring at room temperature. Representative examples of substituentgroups for epoxy resins include halogens, ester groups, ether groups,sulfonate groups, siloxane groups, nitro groups, and phosphate groups.Examples of epoxy resins preferred for this invention include2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane (diglycidyl ether ofbisphenol A) and materials under the trade designation "Epon 828", "Epon1004" and "Epon 1001F", commercially available from Shell Chemical Co.,"DER-331", "DER-332" and "DER-334", commercially available from DowChemical Co. Other suitable epoxy resins include glycidyl ethers ofphenol formaldehyde novolac (e.g., "DEN-431" and "DEN-428", commerciallyavailable from Dow Chemical Co.). The epoxy resins of the invention canpolymerize via a cationic mechanism with the addition of an appropriatephotoinitiator(s). These resins are further described in Smith, U.S.Pat. No. 4,318,766, and Tumey et al., U.S. Pat. No. 4,751,138, both ofwhich are incorporated herein by reference.

Examples of photoinitiators that generate a free radical source whenexposed to ultraviolet light include, but are not limited to, thoseselected from the group consisting of organic peroxides, azo compounds,quinones, benzophenones, nitroso compounds, acyl halides, hydrozones,mercapto compounds, pyrylium compounds, triacrylimidazoles,bisimidazoles, chloroalkytriazines, benzoin ethers, benzil ketals,thioxanthones, and acetophenone derivatives, and mixtures thereof.Examples of photoinitiators that generate a free radical source whenexposed to visible radiation are described in U.S. Pat. No. 4,735,632,incorporated herein by reference.

Cationic photoinitiators generate an acid source to initiate thepolymerization of an epoxy resin or a urethane. Cationic photoinitiatorscan include a salt having an onium cation and a halogen-containingcomplex anion of a metal or metalloid. Other cationic photoinitiatorsinclude a salt having an organometallic complex cation and ahalogen-containing complex anion of a metal or metalloid. Thesephotoinitiators are further described in U.S. Pat. No. 4,751,138,incorporated by reference (col. 6, line 65 through col. 9, line 45).Another example is an organometallic salt and an onium salt described inU.S. Pat. No. 4,985,340 (col. 4, line 65 through col. 14, line 50);European Patent Applications 306,161; 306,162, all of which areincorporated by reference. Still other cationic photoinitiators includean ionic salt of an organometallic complex in which the metal isselected from the elements of Periodic Groups IVB, VB, VIB, VIIB, andVIIIB. This photoinitiator is described in European Patent Application109,581, incorporated herein by reference.

In one particularly useful embodiment, the binder precursor may containabrasive grits. The cured binder precursor, i.e., the binder, functionsto bond the abrasive grits together to form a precisely shaped abrasiveparticle. The abrasive grits typically have an average particle sizeranging from about 0.1 to 1500 micrometers, preferably from about 1 toabout 1300 micrometers, more preferably from about 1 to about 500micrometers, and most preferably from about 1 to about 150 micrometers.It is preferred that the abrasive grits have a Mohs' hardness of atleast about 8, more preferably above 9. Examples of materials of suchabrasive grits include fused aluminum oxide, ceramic aluminum oxide,white fused aluminum oxide, heat treated aluminum oxide, silica, siliconcarbide, green silicon carbide, alumina zirconia, diamond, ceria, cubicboron nitride, garnet, tripoli, and combinations thereof. The ceramicaluminum oxide is preferably made according to a sol gel process, suchas described in U.S. Pat. Nos. 4,314,827; 4,744,802; 4,623,364;4,770,671; 4,881,951; 5,011,508; and 5,213,591, all of which areincorporated herein by reference. The ceramic abrasive grit comprisesalpha alumina and, optionally, a metal oxide modifier, such as magnesia,zirconia, zinc oxide, nickel oxide, hafnia, yttria, silica, iron oxide,titania, lanthanum oxide, ceria, neodynium oxide, and combinationsthereof. The ceramic aluminum oxide may also optionally comprise anucleating agent, such as alpha alumina, iron oxide, iron oxideprecursor, titania, chromia, or combinations thereof. The ceramicaluminum oxide may also have a shape, such as that described in U.S.Pat. Nos. 5,201,916 and 5,090,968, both of which are incorporated hereinby reference. The ceramic abrasive grits may also contain a surfacecoating.

The abrasive grit may also have a surface coating. A surface coating canimprove the adhesion between the abrasive grit and the binder in theabrasive particle and/or can alter the abrading characteristics of theabrasive grit. Such surface coatings are described in U.S. Pat. Nos.5,011,508; 1,910,444; 3,041,156; 5,009,675; 4,997,461; 5,213,591; and5,042,991. An abrasive grit may also contain a coupling agent on itssurface, such as a silane coupling agent.

The binder precursor can contain a single type of abrasive grit, two ormore types of different abrasive grits, or at least one type of abrasivegrit with at least one type of diluent material. Examples of materialsfor diluents include calcium carbonate, glass bubbles, glass beads,greystone, marble, gypsum, clay, SiO₂, KBF₄, Na₂ SiF₆, cryolite, organicbubbles, organic beads, and the like.

The binder precursor for use in this invention can further compriseoptional additives, such as, for example, fillers (including grindingaids), fibers, lubricants, wetting agents, surfactants, pigments, dyes,coupling agents, plasticizers, antistatic agents, and suspending agents.Examples of fillers suitable for this invention include wood pulp,vermiculite, and combinations thereof, metal carbonates, such as calciumcarbonate, e.g., chalk, calcite, marl, travertine, marble, andlimestone, calcium magnesium carbonate, sodium carbonate, magnesiumcarbonate; silica, such as amorphous silica, quartz, glass beads, glassbubbles, and glass fibers; silicates, such as talc, clays(montmorillonite), feldspar, mica, calcium silicate, calciummetasilicate, sodium aluminosilicate, sodium silicate; metal sulfates,such as calcium sulfate, barium sulfate, sodium sulfate, aluminum sodiumsulfate, aluminum sulfate; gypsum; vermiculite; wood flour; aluminumtrihydrate; metal oxides, such as calcium oxide (lime), aluminum oxide,titanium dioxide, and metal sulfites, such as calcium sulfite.

A grinding aid is defined as particulate material the addition of whichto an abrasive article has a significant effect on the chemical andphysical processes of abrading, thereby resulting in improvedperformance. In particular, it is believed that the grinding aid will(1) decrease the friction between the abrasive grits and the workpiecebeing abraded, (2) prevent the abrasive grits from "capping", i.e.,prevent metal particles from becoming welded to the tops of the abrasivegrits, (3) decrease the interface temperature between the abrasive gritsand the workpiece, or (4) decrease the grinding forces. In general, theaddition of a grinding aid increases the useful life of the coatedabrasive article. Grinding aids encompass a wide variety of differentmaterials and can be inorganic or organic. Examples of grinding aidsinclude waxes, organic halide compounds, halide salts, and metals andtheir alloys. The organic halide compounds will typically break downduring abrading and release a halogen acid or a gaseous halide compound.Examples of such materials include chlorinated waxes, such astetrachloronaphthalene, pentachloronaphthalene, and polyvinyl chloride.Examples of halide salts include sodium chloride, potassium cryolite,sodium cryolite, ammonium cryolite, potassium tetrafluoroborate, sodiumtetrafluoroborate, silicon fluorides, potassium chloride, and magnesiumchloride. Examples of metals include tin, lead, bismuth, cobalt,antimony, cadmium, iron, and titanium. Other grinding aids includesulfur, organic sulfur compounds, graphite, and metallic sulfides. It isalso within the scope of this invention to use a combination ofdifferent grinding aids and, in some instances, this may produce asynergistic effect. The above-mentioned examples of grinding aids ismeant to be a representative showing of grinding aids, and it is notmeant to encompass all grinding aids.

Examples of coupling agents suitable for this invention includeorgano-silanes, zircoaluminates, and titanates. Examples of antistaticagents include graphite, carbon black, conductive polymers, humectants,vanadium oxide, and the like. The amounts of these materials can beadjusted to provide the properties desired. The binder precursor canoptionally include water or an organic solvent.

If the particle contains abrasive grits, it is preferred that theparticle be capable of breaking down during abrading. The selection andamount of the binder precursor, abrasive grits, and optional additiveswill influence the breakdown characteristics of the particle.

In order to form a mixture comprising a binder precursor and othermaterials, such as abrasive grits, the components can be mixed togetherby any conventional technique, such as, for example high shear mixing,air stirring, or tumbling. A vacuum can be used on the mixture duringmixing to minimize entrapment of air.

The binder precursor can be introduced to the cavity of the productiontool by a dispensing means that utilizes any conventional technique,such as, for example, gravity feeding, pumping, die coating, or vacuumdrop die coating. The binder precursor can also be introduced to thecavities of the production tool by transfer via a carrier web. Thebinder precursor can be subjected to ultrasonic energy during the mixingstep or immediately prior to the coating step in order to lower theviscosity of the binder precursor.

Although the binder precursor is only required to fill a portion of thecavity, the binder precursor preferably completely fills the cavity inthe surface of the production tool, so that the resulting particulatematerial will contain few voids or imperfections. These imperfectionscause the shape of the particulate material to depart from the desiredprecise shape. Additionally, when the precisely shaped binder materialis removed from the production tool, an edge may break off, therebycreating an imperfection and detracting from the preciseness of theshape. It is preferred that care be taken throughout the process tominimize such imperfections. Sometimes, voids or imperfections aredesirable, because they create porosity in the resultant particles,thereby causing the particles to have greater erodibility. It is alsopreferred that the binder precursor not extend substantially beyond theplane of the continuous surface of the production tool and not extendsubstantially beyond the openings of the cavities of the productiontool.

It is sometimes preferred that the binder precursor be heated prior tobeing introduced to the production tool, typically at a temperature inthe range of from about 40° to 90° C. When the binder precursor isheated, its viscosity is reduced with the result that it can flow morereadily into the cavities of the production tool.

The step following the introduction of the binder precursor into thecavities of the production tool involves at least partially curing thebinder precursor by exposing it to radiation energy or thermal energywhile it is present in the cavities of the production tool.Alternatively, the binder precursor can be at least partially curedwhile it is present in the cavities of the production tool, and thenpost-cured after the binder is removed from the cavities of theproduction tool. The post-cure step can be omitted. The degree of cureis sufficient that the resulting solidified, handleable binder willretain its shape upon removal from the production tool.

Examples of sources of radiation energy for use in the curing zoneinclude electron beam, ultraviolet light, visible light, and laserlight. Electron beam radiation, which is also known as ionizingradiation, can be used at an energy level of about 0.1 to about 20 Mrad,preferably at an energy level of about 1 to about 10 Mrad. Ultravioletradiation refers to non-particulate radiation having a wavelength withinthe range of about 200 to about 400 nanometers, preferably within therange of about 250 to 400 nanometers. The dosage of radiation can rangefrom about 50 to about 1000 mJ/cm², preferably from about 100 mJ/cm² toabout 400 mJ/cm². Examples of lamp sources that are suitable forproviding this amount of dosage provide about 100 to about 600watts/inch, preferably from about 300 to about 600 watts/inch. Visibleradiation refers to non-particulate radiation having a wavelength withinthe range of about 400 to about 800 nanometers, preferably in the rangeof about 400 to about 550 nanometers. The amount of radiation energyneeded to sufficiently cure the binder precursor depends upon factorssuch as the depth of the binder precursor while in the cavity, thechemical identity of the binder precursor, and the type of loadingmaterial, if any. Conditions for thermal cure range from a temperatureof about 50° to about 200° C. and for a time of from fractions tothousands of minutes. The actual amount of heat required is greatlydependent on the chemistry of the binder precursor.

After being at least partially cured, the resulting solidified,handleable binder will preferably not strongly adhere to the surface ofthe production tool. In either case, at this point, the solidifiedbinder precursor is removed from the production tool.

There are several alternative methods for removing the solidified,handleable binder i.e., the binder, from the production tool. In onemethod, the binder is transferred directly from the production tool to acollector, e.g., a hopper. In this method, if the production tool ismade of a polymeric material, the binder can be removed from thecavities by ultrasonic energy, a vacuum, an air knife, or combinationsthereof or other conventional mechanical means. If the production toolis made of metal, the binder can be removed from the cavities by meansof a water jet or air jet. If the production tool has cavities thatextend completely through the production tool, e.g., if the productiontool is a belt having perforations extending completely therethrough,the binder can be removed by ultrasonic energy, mechanical force, waterjet, air jet, or combinations thereof, or other mechanical means,regardless of the material of construction of the production tool.

In another method, the binder can be transferred indirectly from theproduction tool to a collector. In one embodiment, the binder can betransferred from the production tool to a smooth roll. The binderexhibits greater adhesion to the smooth roll than to the productiontool. The transferred binder can then be removed from the smooth roll bymeans of skiving, vacuum, water jet, air jet, or other mechanical means.In one particular embodiment, the binder can be transferred from theproduction tool to a major surface of a carrier web. The binder exhibitsgreater adhesion to the major surface of the carrier web than to theproduction tool. The major surface of the carrier web to which thebinder is transferred can bear a layer of material that is soluble inwater or an organic solvent. The binder can easily be removed from thecarrier web by merely dissolving the material that forms the solublelayer. In addition, mechanical means, e.g., skiving, vacuum, orultrasound, can be used to remove the binder. Ultrasonic energy can beapplied directly over a major surface of the web or off to a side of amajor surface of the web. In another embodiment, the major surface ofthe carrier web can have a primer thereon. Examples of primers suitablefor the carrier web include ethylene acrylic acid copolymer,polyvinylidene chloride, crosslinked hexanediol diacrylate, aziridinematerials, and the like. The binder will preferentially adhere to theprimed carrier web. The binder can then be removed from the primedcarrier web by mechanical means, e.g., skiving, vacuum, or ultrasound.

After the binder is removed from the production tool, either by director indirect means, it is then converted into particles. In one mode ofconversion, the binder is released from the production tool in the formof particles. A given particle will have a shape that is essentially theshape of the portion of the cavity of the production tool in which theparticle was at least partially cured. An advantage of this mode is thatthe particles are already of the proper grade or of the proper particlesize distribution for subsequent use, e.g., incorporation into anabrasive article. In the conventional manner of making abrasiveparticles, e.g., agglomerates, the abrasive particles have to be crushedand then screened to obtain proper particle size distribution.

In a second mode of conversion, the binder is released from theproduction tool as a sheet of material comprising precisely shapedbinder material interconnected by a thin layer of binder material. Thebinder is then broken or crushed along the thin interconnecting portionsto form the particles of this invention.

In a variation, the production tool can be a drum or a belt that rotatesabout an axis. When the production tool rotates about an axis, theprocess can be conducted continuously. When the production tool isstationary, as in processes of the prior art, the process is conductedbatch-wise. The continuous process of this invention is usually moreefficient and economical than the batch-wise processes of the prior art.

This invention also provides abrasive articles containing abrasiveparticles made according to the process of this invention. Theseabrasive articles can be bonded abrasive articles, coated abrasivearticles, or nonwoven abrasive articles. For a bonded abrasive article,the precisely shaped abrasive particles are bonded together by a bondingmedium to form a shaped mass, e.g., a wheel, a cut-off wheel. Bondedabrasive articles are typically made by a molding process. For a coatedabrasive article, the abrasive precisely shaped particles are bonded bya bonding medium to a backing. For a nonwoven abrasive article, theabrasive precisely shaped particles are bonded by a bonding medium intoa nonwoven fibrous substrate.

Backings suitable for preparing coated abrasive articles includepolymeric film, primed polymeric film, cloth, paper, vulcanized fibre,polymeric foam, nonwovens, treated versions thereof, and combinationsthereof. Referring to FIGS. 4 and 5, coated abrasive article 100contains two coatings for binding the abrasive particles to the backing.Coating 102, commonly referred to as a make coat, is applied overbacking 104 and bonds abrasive particles 106 to backing 104. Coating108, commonly referred to as a size coat, is applied over abrasiveparticles 106 and reinforces abrasive particles 106. There may also be athird coating 110, commonly referred to as a supersize coat, appliedover the size coat 108. As mentioned previously, the abrasive particles106 comprise a plurality of abrasive grits 112 and a binder 114. Theabrasive particles can be applied to the backing by conventionaltechniques, e.g., by drop coating or by electrostatic coating. Dependingupon the coating method, the abrasive particles can either be orientedin a non-random manner as in FIG. 4 or oriented in a random manner as inFIG. 5.

The material for bonding the abrasive material to a substrate ortogether comprises a cured resinous adhesive and optional additives.Examples of resinous adhesives suitable for this invention includephenolic resins, aminoplast resins, urethane resins, epoxy resins,acrylate resins, acrylated isocyanurate resins, urea-formaldehyderesins, isocyanurate resins, acrylated urethane resins, vinyl ethers,acrylated epoxy resins, maleimide resins and combinations thereof. Theoptional additives include fillers (including grinding aids), fibers,lubricants, wetting agents, surfactants, pigments, dyes, couplingagents, plasticizers, and suspending agents. Examples of fillers includetalc, calcium carbonate, calcium metasilicate, silica and combinationsthereof. The amounts of these materials are selected to provide theproperties desired.

A nonwoven abrasive article comprises an open, porous, fibrous, nonwovensubstrate having a plurality of abrasive particles bonded into thesubstrate. This type of nonwoven abrasive article is described in U.S.Pat. No. 2,958,593.

The abrasive articles of this invention may further contain conventionalabrasive agglomerates or individual abrasive grits or both. Conventionalabrasive agglomerates are further described in U.S. Pat. Nos. 4,311,489;4,652,275; and 4,799,939, incorporated herein by reference. Individualabrasive grits can also be selected to have a precise shape. Examples ofindividual abrasive grits include fused aluminum oxide, ceramic aluminumoxide, heat treated aluminum oxide, silicon carbide, alumina zirconia,diamond, ceria, cubic boron nitride, garnet, and combinations thereof.At least 10%, preferably at least 50%, and most preferably at least 70%,of the abrasive material should be the precisely shaped abrasiveparticles of this invention. In a coated abrasive article, theindividual abrasive grits can be disposed over the precisely shapedabrasive particles. Alternatively, the individual abrasive grits can bedisposed underneath the precisely shaped abrasive particles. Theindividual abrasive grit can be disposed between two precisely shapedabrasive particles.

It is preferred that the precisely shaped particles have no dimensiongreater than 2500 micrometers. It is preferred that the size of theprecisely shaped particles range from 0.1 to 1500 micrometers, morepreferably from 0.1 to 500 micrometers. As indicated previously, theprecise shape corresponds to portions of the surface of the productiontool, e.g., cavities formed in the surface of the production tool. Theparticles of this invention have a precise shape. This precise shape isattributable to the binder precursor's being at least partially cured inthe cavities of the production tool. There may, however, be minorimperfections in the particles that are introduced when the particlesare removed from the cavities. If the binder precursor is notsufficiently cured in the cavities, the binder precursor will flow, andthe resulting shape will not correspond to the shape of the cavities.This lack of correspondence gives an imprecise and irregular shape tothe particle. This precise shape can be any geometrical shape, such as acone, triangular prism, cylinder, pyramid, sphere, and a body having twoopposed polygonal faces separated by a constant or varying distance,i.e., a polygonal platelet. Pyramids preferably have bases having threeor four sides. The abrasive article may contain a variety of abrasiveparticles having different shapes. FIG. 7 is a scanning electronphotomicrograph taken at about 300 magnification of an abrasive particlein the form of a pyramid having a triangular base.

The weight percentages of the abrasive grits and the binder in theprecisely shaped particle will depend on several factors, such as theintended use of the abrasive article and the particle size anddistribution of the abrasive grit. Typically, the percent by weightabrasive grits will range from about 5 to 95% and the percent by weightbinder will range from about 95 to 5%. Preferably, the percentage, basedon weight, of abrasive grits ranges from 20 to 75% and the percentage ofbinder ranges from 80 to 25%.

In another aspect of this invention, the precisely shaped particles donot contain any abrasive grits. These precisely shaped particles thatare free of abrasive grits can be used in a coated abrasive article as adiluent particle. For example, a coated abrasive article may comprise abacking, and bonded to the backing are abrasive grits and preciselyshaped particles that are free of abrasive grits. Alternatively, thecoated abrasive article may comprise a backing, a first coat of curedresinous adhesive (make coat) applied over the front surface of thebacking, abrasive grits and precisely shaped particles, wherein thegrits and precisely shaped particles are secured to the backing by meansof the make coat. Over the abrasive grits and precisely shaped particlesis a second coat of cured resinous adhesive (size coat).

The precisely shaped abrasive particles can be coated or placed randomlyonto the backing. Alternatively, the precisely shaped abrasive particlescan be oriented on the backing in a specified direction. In the case ofprecisely shaped particles having the shapes of pyramids, cones, andprisms (e.g., triangular-shaped prisms), the particles can be orientedso that their bases point toward the backing and their vertexes pointaway from the backing, as in FIG. 4, or they can be oriented so thattheir vertexes point toward the backing and their bases point away fromthe backing, as do four of the particles in FIG. 5. With respect topyramids and cones, the vertex referred to is the common vertex.

The coated abrasive article can be made according to the followingprocedure. A backing having a front surface and a back surface isprovided. The front surface of the backing is coated with a firstcurable bonding medium comprising a resinous adhesive; then theprecisely shaped abrasive particles and, optionally, the individualabrasive grits are coated or applied into the first curable bondingmedium. The precisely shaped abrasive particles and optional abrasivegrits can be drop coated or electrostatic coated. The first curablebonding medium is then solidified or cured to form a cured resinousadhesive. Optionally, a second curable bonding medium comprising aresinous adhesive can be applied over the precisely shaped abrasiveparticles and then solidified or cured to form a cured resinousadhesive. The second curable bonding medium can be applied prior to orsubsequent to solidification or curing of the first curable bondingmedium.

It is within the scope of this invention to provide a coating on theouter surface of the precisely shaped particle. The coating can becontinuous or discontinuous. Examples of coatings suitable for theparticles include metal coatings, metal oxide coatings, carbidecoatings, nitride coatings, boride coatings, carbon coatings, diamondcoatings, diamond like carbon coatings, and the like. Alternatively anorganic coating can be present on the surface of the particle. Theorganic coating may also contain fillers, coupling agents, antistaticagents, grinding aids, and the like. The selection and amount of thecoating will depend upon the desired properties of the particle. Forinstance, some coatings will result in a retro-reflective particle.Alternatively, some coatings will improve adhesion of the particle toother materials or a substrate.

The following non-limiting examples will further illustrate theinvention. All parts, percentages, ratios, etc, in the examples are byweight unless indicated otherwise.

The following abbreviations and trade names are used throughout theexamples.

    ______________________________________                                        TATHEIC triacrylate of tris(hydroxy ethyl)                                            isocyanurate                                                          PH1     2,2-dimethoxy-1-2-diphenyl-1-ethanone,                                        commercially available from Ciga Geigy                                        Company under the trade designation "IRGACURE                                 651"                                                                  PH2     2-benzyl-2-N,N-dimethylamino-1-(4-                                            morpholinophenyl)-1-butanone, commercially                                    available from Ciba Geigy Company under the                                   trade designation "IRGACURE 369"                                      WAO1    white aluminum oxide, 40 micrometer grade                                     distribution                                                          WAO2    white aluminum oxide, grade P-100                                     TMPTA   trimethylol propane triacrylate                                       MSCA    3-methacryloxypropyl-trimethoxy silane                                        coupling agent, commercially available from                                   Union Carbide Corp. under the trade                                           designation "A-174"                                                   ASF     amorphous silica particles having an average                                  surface area of 50 m.sup.2 /g, commercially                                   available from DeGussa Corp. (Richfield Part,                                 NJ), under the trade designation "OX-50"                              PH3     neopentyl glycol propoxylate diacrylate,                                      commercially available from Henkel Corp.                                      (Ambler, PA), under the trade designation                                     "Photomer 4127"                                                       HMPP    2-hydroxy-2-methyl-1-phenyl-propan-1-one,                                     commercially available from Ciba Geigy                                        Company, under the trade designation "Darocur                                 1173"                                                                 IOA     isooctyl acrylate, commercially available                                     from CPS Chemicals (West Memphis, AR)                                 UDO     aliphatic urethane diacrylate oligomer,                                       diluted 15% with tripropylene glycol                                          diacrylate, commercially available from                                       Radcure Specialties, Inc. (Louisville, KY),                                   under the trade designation "Ebecryl 4883"                            ACU     acrylate urethane containing 25% hexandiol                                    diacrylate, commercially available from                                       Cargill, Inc. (Minneapolis, MN), under the                                    trade designation "15-1525"                                           APC     hydrolyzed form of 3-(trimethoxysilyl)-                                       propylmethacrylate                                                    ______________________________________                                    

The abrasive particles were made according to one of the generalprocedures for preparing abrasive particles described below. Abrasiveparticles prepared by the methods of this invention were incorporatedinto a coated abrasive article according to the General Procedure ForMaking a Coated Abrasive Article described below. The abrasive articleswere tested according to one of the test procedures described below.

General Procedure I for Preparing Abrasive Particles

A mixture containing TATHEIC (50 parts), TMPTA (50 parts), PH1 (2parts), MSCA (0.5 part), and WAO1 (200 parts) having an average particlesize 40 micrometers was coated onto the surface of a production toolhaving a pattern having cavities formed therein, which cavities can becharacterized as being inverted pyramids. The tool was made of nickeland was essentially in the form of a sheet. The tool was made of nickeland was essentially in the form of a sheet. A sufficient amount ofmixture was used to fill the cavities of the production tool. Thepyramids of the pattern were disposed such that their bases were buttedup against one another. The length of the base of the pyramid was about530 micrometers and the height of the pyramid was about 530 micrometers.This type of pattern is illustrated in FIG. 1 of U.S. Pat. No.5,152,917. Next, a polyester film (polyethylene terephthalate; 130micrometers thick) was pressed against the production tool by means of aroller, and the mixture wetted the front surface of the polyester film.The front surface of the polyester film contained an ethylene acrylicacid prime coating having a thickness of about 20 micrometers. Then,ultraviolet light was transmitted through the polyester film and intothe mixture to initiate polymerization of the binder precursor. Thesource of ultraviolet light consisted of two Aetek medium pressuremercury lamps, operating at 300 watts/inch. Next, the polyester film wasseparated from the production tool. The resulting abrasive particles,which preferentially adhered to the polyester film, were then removedfrom the polyester film by mechanical means. Then, the abrasiveparticles were forced through a 850 micrometer screen to separateabrasive particles that were adhered to one another, thereby formingindividual abrasive particles.

General Procedure II for Preparing Abrasive Particles

General Procedure II was similar to General Procedure I with thefollowing exceptions.

A binder precursor was prepared by mixing a composition consisting of29.5 parts of a 50:50:1 mixture of TMPTA:TATHEIC:PH2 and 0.5 part of APCwith 69 parts WAO1 and 1 part ASF. A bead of the binder precursor waspoured onto the production tool, which was the same as that used inGeneral Procedure I for preparing abrasive particles. The carrier webwas placed primer side down on the binder precursor and production tool.A plastic blade was applied to the backside of the carrier web tosqueeze the binder precursor into the cavities of the tool. The carrierweb/precursor/production tool construction was then taped to a metalplaten, polyester side up, and was irradiated at a speed of about 3.1meters/minute. The source of radiation energy was a 600 watt "V" bulb(available from Fusion Systems) on high setting. A nitrogen purge wasused.

General Procedure for Preparing Coated Abrasive Articles for ComparativeExamples

Coated abrasive articles were made according to the teachings of U.S.Pat. No. 5,152,917, incorporated herein by reference. A mixturecontaining abrasive grits and binder precursor was coated onto aproduction tool. The production tool had cavities having the shape ofinverted pyramids. The pyramids were disposed such that their bases werebutted up against one another. The length of the pyramid base was about530 micrometers and the height of the pyramid was about 530 micrometers.This type of pattern is illustrated in FIG. 1 of U.S. Pat. No.5,152,917. The mixture was applied in a manner so as to fill thecavities. Next, a polyester film (80 micrometers thick) was pressedagainst the production tool by means of a roller, and the mixture wettedthe front surface of the polyester film. The front surface of thepolyester film contained an ethylene acrylic acid primer. Thenultraviolet light was transmitted through the polyester film and intothe mixture to initiate polymerization of the binder precursor. Themixture was transformed into an abrasive composite. The source ofultraviolet light consisted of two Aetek medium pressure mercury lamps,operating at 300 watts/inch. Next, the polyester film/abrasive compositewas separated from the tool to form an abrasive article. This processwas a continuous process that was run at about 2.4 meters/minute. Next,the resulting abrasive article was laminated to vulcanized fibre (about0.8 millimeter thick) by means of double stick tape.

General Procedure for Preparing Coated Abrasive Articles of thisInvention (Disc)

The abrasive particles were incorporated into a coated abrasive dischaving a backing made of vulcanized fibre. These fibre discs wereindividually made and had a diameter of 17.8 cm with a center holehaving a diameter of 2.2 cm. The make coat was a conventional calciumcarbonate filled phenolic resin (48% resin, 52% CaCO₃). The abrasiveparticles were electrostatically coated into the make coat. The sizecoat was also a conventional calcium carbonate filled phenolic resin(48% resin, 52% CaCO₃). The fibre discs were flexed prior to testing.The wet make coat weight was approximately four grams/disc and the wetsize coat weight was approximately seven grams/disc.

General Procedure for Preparing Coated Abrasive Articles of thisInvention (Belt)

The abrasive particles were incorporated into an endless coated abrasivebelt having a spliceless backing as taught in U.S. Ser. No. 07/919,541,filed Jul. 24, 1992, now abandoned incorporated herein by reference. Themake coat was a conventional calcium carbonate filled phenolic resin(48% resin, 52% CaCO₃). The abrasive particles were drop coated onto thebacking at a coating weight of 80 grains per 10 cm×15 cm sample. Thesize coat was also a conventional calcium carbonate filled phenolicresin (48% resin, 52% CaCO₃). The belts were flexed prior to testing.

Test Procedure I

The coated abrasive disc was first mounted on a beveled aluminum back-uppad and then used to grind the face of a 1.25 cm by 18 cm 1018 mildsteel workpiece. The disc was driven at 5,500 rpm while the portion ofthe disc overlaying the beveled edge of the back-up pad contacted theworkpiece at a load of about 4.5 kg. Each disc was used to grind aseparate workpiece for one minute intervals for a total grinding time offive minutes. The amount of metal removed during each one minuteinterval was recorded.

Test Procedure II

Test Procedure II was the same as Test Procedure I, except for thefollowing changes. The load was 300 grams; the test was ended when theworkpiece began to burn, i.e., turn black or blue; and the grindinginterval was 30 seconds. The initial cut for Test Procedure II was theamount of material removed after 30 seconds of grinding. The final cutfor Test Procedure II was the amount of material removed in the last 30seconds of grinding. The total cut is the sum of the cut throughout thetest.

Test Procedure III

The coated abrasive article was converted into a 7.6 cm by 335 cmendless belt and tested on a constant load surface grinder. Apre-weighed 4150 mild steel workpiece, approximately 2.5 cm by 5 cm by18 cm, was mounted in a holder. The workpiece was positioned vertically,with the 2.5 cm by 18 cm face facing an approximately 36 cm diameterserrated rubber contact wheel (85 Shore A durometer) with one-on-onelands over which was entrained the coated abrasive belt. The workpiecewas reciprocated vertically through an 18 cm path at the rate of 20cycles per minute, while a spring loaded plunger urged the workpieceagainst the belt with a load of about 6.8 kg as the belt was driven atabout 2050 meters per minute. After one minute elapsed grinding time,the workpiece holder assembly was removed and re-weighed, the amount ofstock removed calculated by subtracting the weight after abrading fromthe original weight, and a new, pre-weighed workpiece and holder weremounted on the equipment. Approximately two belts were tested.

EXAMPLE 1

The particles for Example 1 were prepared on the apparatus illustratedin FIG. 8. Apparatus 120 comprised a production tool 122 in the form ofweb, which was fed from a first unwind station 124. Unwind station 124was in the form of a roll. The production tool 122 was made of apolymeric material that was transparent to radiation. The productiontool was made of a polymer having a polyethylene backbone andfluoroaliphatic groups attached thereto. This polymer is furtherdescribed in WO 92-15626, published Sep. 17, 1990. The ethylene polymerwas bonded to polyester and was characterized by a pattern of cavitiesin the form of pyramids having square bases and disposed such that thebases were butted up against each other. The height of the pyramid wasabout 500 micrometers and the length of each side of the base was about900 micrometers. The surface of the production tool containing thecavities is similar to the segment of the production tool shown in FIG.6. As the production tool 122 left the unwind station 124, a carrier web126 left a second unwind station 128. The carrier web 126 was made of apolyvinyl alcohol coated paper, commercially available from SchoellerTechnical Papers, Inc. of Pulaski, N.Y.; stock number 89-844. A binderprecursor 130 was applied by means of a coater 132 into the cavities ofthe production tool 122. The binder precursor consisted of ACU (65parts), PH3 (35 parts), HMPP (1 part). The portion of the productiontool 134 containing the binder precursor was brought into contact withthe carrier web 126 by means of a nip roll 136. The portion of theproduction tool 134 containing the binder precursor and the carrier web126 was forced against a mandrel 138. The mandrel 138 rotated about anaxis 140. Next, radiation energy from radiation source 141 in a curingzone 142 was transmitted through the production tool 122 and into thebinder precursor. The source of radiation energy was a medium pressuremercury vapor ultraviolet lamp operating at 300 watts/inch (120watts/cm). Upon exposure to the energy source, the binder precursor wasconverted into a solidified, handleable binder. Both the production toolcontaining the solidified, handleable binder and the carrier web werecontinuously moved through the curing zone 142 by means of the mandrel138. The carrier web 126 was separated from the production toolcontaining the binder in the vicinity of a nip roll 143. The carrier web126 was rewound on a rewind station 144.

The process was continuous and operated at a web speed of 3.1meters/minute. After curing, the polyvinyl alcohol coated paper havingparticles bonded thereto was removed from the apparatus and the exposedfaces of the particles were coated with aluminum by means of a cathodicarc. The thickness of the coating was 600 Angstroms. The polyvinylalcohol layer was then stripped from the paper backing, dissolved inwater (100° C.) with stirring for three minutes. The particles were thencollected by vacuum filtration. The coated particles possessed thenecessary mirrored retroreflection needed from low index materials toprovide a greater angularity and function as good retroreflectors.

EXAMPLE 2

The particles for Example 2 were prepared on the apparatus illustratedin FIG. 9. Apparatus 160 comprised a production tool 162 in the form ofan endless belt, which traversed a series of rollers 164, at least oneof which was power-driven. The production tool 162 was made of the samematerial as was the production tool in Example 1 and was characterizedby a pattern of pyramids having triangular bases and disposed such thatthe bases were butted up against each other. The height of the pyramidwas about 75 micrometers and the length of each side of the base wasabout 125 micrometers. A binder precursor 166 was applied by means of aknife coater 168 into the cavities of the production tool 162.

The binder precursor consisted of UDO (67 parts), IOA (28 parts), MSCA(4 parts), and HMPP (1 part). The binder precursor 166 then traveledthrough a curing zone 170 where it was exposed to a source of radiationenergy 172. The source of radiation energy was a medium pressure mercuryvapor ultraviolet lamp operating at 300 watts/inch (120 watts/cm). Theprocess was continuous and operated at a web speed of 0.6 meter/minute.Upon exposure to the energy source 172, the binder precursor 166 wasconverted into a solidified, handleable binder. The particles of binder178 preferentially adhered to a smooth-surfaced roll 174. Immediatelyafter leaving the curing zone 170, the particles 178 were removed fromthe smooth-surfaced roll 174 by a skiving means 176 and collected bymeans of vacuum (not shown). The particles 178 were then tumble vaporcoated with silver by the following process. While the precisely shapedparticles (8.0 g) were being tumbled in a vacuum chamber, they weresputter-coated with silver vapor from a sputtering target. The circularsilver target (5 cm diameter and 0.4 cm thick) was attached to a Model200 US' Gun from US, Inc. (Campbell, Calif.). The sputter gun wasoperated for 105 minutes in a direct current, planar magnetron mode atan applied power of 0.10 kilowatts, with a resulting cathode potentialin the range of 476 to 502 volts. The argon sputtering gas pressure wasapproximately 6 millitorr and the background pressure was 8×10⁻⁶ torr.The resulting precisely shaped particles were silver colored and had abulk powder resistivity of 0.3 ohm-cm. The coated particles possessed ahighly specular reflective coating, rendering them suitable for use insignage and reflective outerwear.

EXAMPLES 3-9

The particles in Example 3 were prepared according to General ProcedureI for Preparing Abrasive Particles, with the exception that PH2 was usedinstead of PH1. The precisely shaped particles for Examples 3-9 wereremoved from the carrier web by ultrasonic energy. More particularly,the backside of the carrier web was pulled, under tension, across theforward edge of an ultrasonic horn tapered to a single edge. The hornwas oscillated at a frequency of 19,100 HZ at an amplitude of about 130micrometers. The horn was composed of 6-4 titanium and was driven with a900 watt 184V Branson power source coupled with a 2:1 Booster 802piezoelectric converter.

The following table sets forth the construction of the carrier web ofeach of Examples 3-9. The particles in Examples 4-9 were preparedaccording to General Procedure II for Preparing Abrasive Particles.

                  TABLE 1                                                         ______________________________________                                                Base of Thickness  Primer of                                                                              Thickness                                         carrier of base    carrier  of primer                                 Example web.sup.1                                                                             (μm)    web.sup.2                                                                              (μm)                                   ______________________________________                                        3       PET     130        EAA      13                                        4       PET     100        PVA      13                                        5       PET     130        EAA/PVA.sup.3                                                                          20/13.sup.3                               6       PET     100        PVDC     --                                        7       PET     265        HDDA     --                                        8       PET      76        Aziridine +                                                                            --                                                                   sulfo-                                                                        polyester                                          9       PET      76        Aziridine                                                                              --                                        ______________________________________                                         .sup.1 PET means polyethylene terephthalate                                   .sup.2 EAA means ethylene acrylic acid; PVA means polyvinyl alcohol; PVDC     means polyvinylidene chloride; HDDA means hexanediol diacrylate               .sup.3 The primer consisted of an undercoat of EAA (20 μm) and a top       coat of PVA (13 μm).                                                  

Table 2 sets forth the assessment of removal of the particles from thecarrier web. Two procedural embodiments were tested: (1) directlyrunning the film across the ultrasonic horn, and (2) heating the carrierweb and composites at 115° C. for 10 minutes before running the filmacross the ultrasonic horn.

                  TABLE 2                                                         ______________________________________                                               Assessment of Removal                                                  Example  Untreated Samples                                                                             Heated Samples                                       ______________________________________                                        3        facile          difficult where EAA                                                           was melted and fixed                                                          composites to film                                   4        --              PVA removed from                                                              film with composites                                 5        --              facile                                               6        facile          facile                                               7        facile          facile                                               8        facile          film breaks                                          9        facile          facile                                               ______________________________________                                    

EXAMPLES 10-13

Examples 10-13 demonstrate the use of water soluble primers for theremoval of the particles from the carrier web.

EXAMPLE 10

The particles for Example 10 were prepared according to GeneralProcedure II for Preparing Abrasive Particles, with the exception thatthe production tool was a transparent silicone tool having the sametopography as the nickel production tool. The binder precursor was curedthrough the transparent tool by means of a 600 watt "V" bulb (FusionSystems) on "high setting" at a rate of 3.1 meters/minute. The carrierweb was a release paper having a 13 micrometer thick coating ofpolyvinyl alcohol, available from Schoeller Technical Papers, Inc. Afterthe binder precursor was cured, the sandwich construction was peeledapart. The carrier web with the solidified particles adhering theretowas placed under tap water, the particles were released from thebacking, and the individual particles were recovered by mechanicalprocessing.

EXAMPLE 11

The particles for Example 11 were prepared according to GeneralProcedure II for Preparing Abrasive Particles. A coated release liner asdescribed in Example 10 was laminated to unprimed 100 micrometerpolyester terephthalate film by a pair of heated nip rolls in a mannersuch that the polyvinyl alcohol coating was transferred from the releasepaper to the film. The primed film was used as the carrier web. Afterthe binder precursor was cured, the sandwich construction was peeledapart. The carrier web with the solidified particles adhering theretowas placed under tap water, the particles were released from thebacking, and the individual particles were recovered by mechanicalprocessing.

EXAMPLE 12

Example 11 was repeated, with the sole exception being that the unprimedpolyethylene terephthalate film was 130 micrometers thick and had apolyvinylidene chloride prime coat.

EXAMPLE 13

Example 12 was repeated, with the sole exception being that thepolyethylene terephthalate film had been primed with ethylene acrylicacid (13 μm).

EXAMPLE 14 AND COMPARATIVE EXAMPLES A AND B

The abrasive particles of Example 14 was made according to GeneralProcedure I for Preparing Abrasive Particles. The coated abrasivearticle for Example 14 was prepared according to General Procedure forPreparing Coated Abrasive Articles of this Invention (Disc).

Comparative Example A employed a conventional lapping film (40micrometer, 3M 268L Imperial Microfinishing Film, commercially availablefrom Minnesota Mining and Manufacturing Company, St. Paul, Minn.). Thiscoated abrasive article was laminated to a vulcanized fibre backing (0.8millimeter thick).

Comparative Example B employed a conventional three-dimensional coatedabrasive article (P400 Multicut XF cloth coated abrasive, commerciallyavailable from Minnesota Mining and Manufacturing Company, St. Paul,Minn.). This product contained conventional abrasive agglomerates madeaccording to the teachings of U.S. Pat. No. 4,652,275. This coatedabrasive article was laminated to a vulcanized fibre backing (0.8millimeter thick).

The article of Example 14 was tested according to Test Procedure I andthe test results are set forth in Table 3. The articles of Example 3 andComparative Examples A and B were tested according to Test Procedure II,and the test results are set forth in Table 4.

                  TABLE 3                                                         ______________________________________                                        Time       Amount of metal removed                                            (minutes)  (grams)                                                            ______________________________________                                        1          7                                                                  2          6                                                                  3          6                                                                  4          5                                                                  5          5                                                                  ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                 Initial cut   Final cut                                                                              Total cut                                     Example  (grams)       (grams)  (grams)                                       ______________________________________                                        14       1.7           1.0      27.2                                          Comp. A  1.7           0.3      2.9                                           Comp. B  1.5           0.3      8.4                                           ______________________________________                                    

EXAMPLE 15 AND COMPARATIVE EXAMPLES C AND D

The abrasive article of Example 15 was made in the same manner as wasthe abrasive article of Example 14, except for the following changes.The abrasive grit was WAO2. Additionally, the length of the base of thepyramid and height of the pyramid was about 710 micrometers.

The abrasive article of Comparative Example C was a P100 Regal ResinBond fibre disc, commercially available from Minnesota Mining andManufacturing Company, St. Paul, Minn. This product containsconventional single ceramic aluminum oxide abrasive grains ("Cubitron",available from Minnesota Mining and Manufacturing Company) bonded to avulcanized fibre backing.

The abrasive article of Comparative Example D was made according to theGeneral Procedure for Preparing Coated Abrasive Articles for ComparativeExamples. The mixture for preparing the abrasive particles forComparative Example D was prepared by mixing together TATHEIC (50parts), TMPTA (50 parts), PH1 (2 parts), and WAO2 (200 parts).

The abrasive articles from Example 15 and Comparative Examples C and Dwere tested according to Test Procedure II. The test was ended when theworkpiece was burned. The test results are set forth in Table 5.

                  TABLE 5                                                         ______________________________________                                                 Initial cut   Final cut                                                                              Total cut                                     Example  (grams)       (grams)  (grams)                                       ______________________________________                                        15       6.2           1.8      83                                            Comp. C  10.6          3.4      95                                            Comp. D  5.9           1.6      37                                            ______________________________________                                    

The coated abrasive article of Example 15 performed better than did thecoated abrasive article of Comparative Example D and nearly as well asdid the coated abrasive article of Comparative Example C.

EXAMPLE 16 AND COMPARATIVE EXAMPLES E AND F

The abrasive article of Example 16 was made in the same manner as wasthe abrasive article of Example 14, except for the following changes.The photoinitiator used was PH2, and the length of the base of thepyramid and height of the pyramid was about 710 micrometers.Additionally, an endless coated abrasive belt was made according toGeneral Procedure for Preparing Coated Abrasive Articles of thisInvention (Belt).

The abrasive article of Comparative Example E was a P400 Regal MulticutResin Bond belt, 3M 359F, commercially available from Minnesota Miningand Manufacturing Company, St. Paul, Minn. This product containedconventional ceramic aluminum oxide grain agglomerates ("Cubitron").

The abrasive articles from Example 16 and Comparative Example E weretested according to Test Procedure III. The test results are set forthin Table 6.

                  TABLE 6                                                         ______________________________________                                                                  Comparative                                                 Example 16        Example E                                           Time      Cut    Total Cut    Cut  Total cut                                  (min)     (g)    (g)          (g)  (g)                                        ______________________________________                                         1        1.82   1.82         3.06 3.06                                        2        3.46   5.28         5.66 8.72                                        3        4.47   9.75         6.66 15.38                                       4        4.39   14.14        7.16 22.54                                       5        4.97   19.11        7.19 29.73                                       6        5.45   24.56        7.75 37.48                                       7        6.48   31.03        8.55 46.03                                       8        6.43   37.46        8.36 54.39                                       9        6.33   43.78        8.05 62.44                                      10        6.98   50.76        6.74 69.18                                      11        7.53   58.29        6.05 75.23                                      12        8.38   66.67        4.13 79.36                                      13        8.65   75.32        2.67 82.03                                      14        8.22   83.54        2.15 84.18                                      15        7.39   90.94        1.88 86.06                                      16        8.51   99.45        1.76 87.82                                      17        8.88   108.32       0.94 88.76                                      18        8.74   117.05       0.65 89.41                                      19        8.88   125.94       1.09 90.50                                      20        8.07   134.01       0.93 91.43                                      ______________________________________                                    

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

What is claimed is:
 1. A coated abrasive article comprising:(a) abacking; (b) at least one layer comprising a plurality of preciselyshaped abrasive composites that comprise abrasive grits and a binderformed from a free radically polymerizable binder precursor, whereinsaid precisely shaped composites have vertexes, and wherein theprecisely shaped composites are randomly disposed on the backing suchthat at least a portion of said particles are oriented with saidvertexes point toward said backing; (c) a bonding medium which serves toadhere said precisely shaped particles to said backing.
 2. A coatedabrasive article according to claim 1, wherein said backing is selectedfrom the group consisting of paper, nonwoven substrates, polymeric film,primed polymeric film, cloth, vulcanized fiber, and combinationsthereof.
 3. A coated abrasive article according to claim 1, wherein saidabrasive grits are selected from the group consisting of fused aluminumoxide, ceramic aluminum oxide, heat treated aluminum oxide, siliconcarbide, alumina zirconia, diamond, ceria, cubic boron nitride, garnet,and combinations thereof.
 4. A coated abrasive article according toclaim 1, wherein the size of said precisely shaped composites rangesfrom about 0.1 to about 2500 micrometers.
 5. A coated abrasive articleaccording to claim 1, wherein the size of said precisely shapedcomposites ranges from about 0.1 to about 500 micrometers.
 6. A coatedabrasive article according to claim 1, wherein said precisely shapedcomposites have shapes selected from the group consisting of pyramids,cones, and prisms.
 7. A coated abrasive article according to claim 1,wherein said precisely shaped composites are triangular-based pyramids.8. A coated abrasive article according to claim 1, wherein saidprecisely shaped composites are quadrilateral-based pyramids.
 9. Acoated abrasive article according to claim 1, wherein said binderprecursor is selected from the group consisting of acrylated urethaneresins, ethylenically unsaturated resins, aminoplast resins havingpendant unsaturated carbonyl groups, isocyanurate derivatives having atleast one pendant acrylate group, and isocyanate derivatives having atleast one pendant acrylate group.
 10. A coated abrasive articleaccording to claim 1, wherein said binder precursor further comprises afree radical initiator.
 11. A coated abrasive article according to claim1, wherein said precisely shaped composites further comprise at leastone additive selected from the group consisting of fillers, grindingaids, fibers, antistatic agents, lubricants, wetting agents,surfactants, pigments, dyes, coupling agents, plasticizers, andsuspending agents.
 12. A coated abrasive article according to claim 1,wherein said precisely shaped composites comprise from 5 to 95% byweight abrasive grits and from 95 to 5% by weight binder.
 13. A coatedabrasive article according to claim 1, wherein said precisely shapedcomposites comprise from 20 to 75% by weight abrasive grits and from 80to 25% by weight binder.
 14. A coated abrasive article according toclaim 1, wherein said bonding medium comprises a resinous adhesive. 15.A coated abrasive article according to claim 14, wherein said resinousadhesive is selected from the group consisting of phenolic resins, epoxyresins, urea-formaldehyde resins, acrylate resins, acrylated epoxyresins, acrylated urethane resins, aminoplast resins having pendantalpha, beta unsaturated carbonyl groups, maleimide resins, and urethaneresins.
 16. A coated abrasive article according to claim 1, furthercomprising individual abrasive grits bonded to said backing by means ofsaid bonding medium.
 17. A coated abrasive article according to claim16, wherein said individual abrasive grits are disposed over saidprecisely shaped composites.
 18. A coated abrasive article according toclaim 16, wherein said individual abrasive grits are disposed underneathsaid precisely shaped composites.
 19. A coated abrasive articleaccording to claim 16, wherein said individual abrasive grits aredisposed between said precisely shaped composites.
 20. A coated abrasivearticle according to claim 16, wherein said individual abrasive gritsare precisely shaped.
 21. A coated abrasive article according to claim16, further comprising a second bonding medium applied over saidprecisely shaped composites and said individual abrasive grits.
 22. Acoated abrasive article according to claim 1, wherein at least a portionof said composites are oriented such that said vertexes point away fromsaid backing.